MAINTENANCE OF BOVINE OOCYTES IN MEIOTIC ARREST AND SUBSEQUENT DEVELOPMENT IN-VITRO - A COMPARATIVE-EVALUATION OF ANTRAL FOLLICLE CULTURE WITH OTHER METHODS

The frequency of development of bovine embryos produced by maturation, fertilization, and culture in vitro is lower than that observed in vi vo. One factor that may affect both the frequency of development and t he quality of the embryos produced is the developmental competence of the oocyte. In current in vitro production systems, oocyte maturation, characterized by the resumption of meiosis, occurs after oocyte aspir ation from the follicle. The developmental competence of individual oo cytes may be improved by inducing maturation after culturing under con ditions that inhibit the resumption of meiosis. In order to test this hypothesis, a system has been established in which intact antral folli cles (3-8 mm in diameter) are cultured in vitro. During this period th e oocytes are maintained at the germinal vesicle (CV) stage under the inhibitory effects of the follicle. Culture of intact antral follicles was compared with two other ''physiological'' methods for the mainten ance of CV arrest: oocytes were cultured attached to a small part of t he follicle wall or within hemisections of follicles. It was found tha t 96.8% of oocytes recovered from intact antral follicles-as compared to 24.6% attached to a small part of the follicle wall and 62.7% withi n hemisections of follicles-were maintained at the CV stage after 24-h culture. The effects on GV arrest and subsequent maturation of the oo cytes were evaluated after longer periods of antral follicle culture ( 2, 4, and 7 days). As the culture period increased, the number of CV-a rrested oocytes decreased; the maximum percentage of CV arrest was obs erved after 24-h culture. The majority of these oocytes matured to met aphase II. A comparison of blastocyst production was made after fertil ization and subsequent development of oocytes obtained following folli cle culture and of control oocytes aspirated directly from antral foll icles. The cleavage rate and percentage of blastocyst production in th ese two groups were 54.6 +/- 13.9%, 48.4 +/- 8.4% and 68.6 +/- 8.6%, 3 2.8 +/- 10.8%, respectively. Statistical analysis showed significant d ifferences in both cleavage rate and blastocyst production between the se two groups. Total cell numbers in the control group were 144.6 +/- 7.28 and 152.0 +/- 25.8 after follicle culture. It is concluded that c ulture of intact antral follicles for 24 h is an alternative method fo r the maintenance of bovine oocytes in meiotic arrest and that these o ocytes acquire a greater developmental competence in vitro.